Soldered superconductor with hard insulation

Abstract

A method for the fabrication of an insulated solder bonded multifilamentary superconducting wire composite. An uninsulated wire composite is prepared by using a high melting point solder to join a multifilamentary superconducting composite to a solderable metallic component. A polymer insulation film coating is then applied on top of the wire composite, and the resulting assembly is subjected to heating in a furnace at furnace temperatures and for a period sufficient to cure the insulation but insufficient to melt the solder.

1 . A method for the fabrication of an insulated solder bonded multifilamentary superconducting wire composite, comprising the steps of:
 (a) creating an uninsulated wire composite by using a high melting point solder to join a multifilamentary superconducting composite to a solderable metallic component;   (b) applying a polymer insulation film coating on top of the wire composite from step (a); and   (c) subjecting the assembly from step (b) to heating in a furnace at furnace temperatures and for a period sufficient to cure the said insulation but insufficient to melt the said solder.   
     
     
         2 . A method in accordance with  claim 1 , wherein the high melting point solder is predominately Sn, with one or more alloying metals selected from the group consisting of Sb, Ag, and Cu. 
     
     
         3 . A method in accordance with  claim 2 , wherein the melting point of the solder is above 200° C. and less than 300° C. 
     
     
         4 . A method in accordance with  claim 3 , wherein the high melting point solder is Sn 5 wt % Sb. 
     
     
         5 . A method in accordance with  claim 1 , wherein the multifilamentary composite comprises Nb—Ti alloy filaments in a copper matrix. 
     
     
         6 . A method in accordance with  claim 1 , wherein the multifilamentary composite comprises Nb—Ti alloy filaments in a Cu—Ni alloy matrix. 
     
     
         7 . A method in accordance with  claim 1 , wherein the multifilamentary superconducting composite has a round cross-section. 
     
     
         8 . A method in accordance with  claim 7 , wherein the soldered composite is made by wrapping Cu strip around a round wire. 
     
     
         9 . A method in accordance with  claim 7 , wherein the soldered composite is made by the “wire in channel process” of soldering round wire into a round groove in a generally rectangular shaped channel. 
     
     
         10 . A method in accordance with  claim 9  wherein the solderable metallic channel is pure Cu, Cu alloy, or a Cu clad metal. 
     
     
         11 . A method in accordance with  claim 1  wherein the multifilamentary superconducting composite has a generally rectangular cross-section. 
     
     
         12 . A method in accordance with  claim 11  wherein the soldered composite is made by soldering rectangular (flat) wire to rectangular Cu, Cu alloy, or a Cu clad metal strip. 
     
     
         13 . A method in accordance with  claim 1  wherein the polymer coating is a Formvar® (modified polyvinyl acetal resin) varnish insulation. 
     
     
         14 . A method in accordance with  claim 1  wherein the polymer coating is selected from the group consisting of epoxy, enamel, nylon or varnish type insulations with a curing temperature of over 300° C. 
     
     
         15 . A method in accordance with  claim 1 , where after application of the insulation, the entire composite is drawn and/or shaped into a desired configuration. 
     
     
         16 . A method in accordance with  claim 1  wherein the application of the polymer insulation is by extrusion. 
     
     
         17 . A method in accordance with  claim 16 , wherein the polymer used is an extrudable one selected from the group consisting of nylon, epoxy, PVC, polyethylene and fluoro-chloro-carbon polymers. 
     
     
         18 . A method in accordance with  claim 1 , wherein the surface solder, but not the solder bonding the wire to the channel, is removed prior to application of the insulation by electroplating off the solder. 
     
     
         19 . A method in accordance with  claim 1 , wherein the surface solder is roughened by sandblasting, grit blasting, or embossing.